Hipothalamic hormones, especially prolactin release inhibiting factor (PIF), somatostatin, and growth hormone releasing factor or hormone (GH-RH) will be investigated for identity (PIF and GH-RH) and physiological role (somatostatin). purification of hypothalamic PIF activity has indicated that the most active fraction contains a high percentage of catecholamines which suppress prolactin release from the pituitary by direct action. Other PIF fractions have weaker PIF activity than catecholamines. A concentration of catecholamines in the hypophysial portal blood will be determined in the rat to examine whether the concentration is in a range sufficient to suppress prolactin release. This will provide evidence for or against the possibility that catecholamines represent physiological PIF. Another study will be aimed at clarifying the physiological role of somatostatin by neutralizing endogenous somatostatin's influence by passive or active immunization. For screening GH-RH activity, sheep immunogamma globulin against somatostatin will be coupled with CN-BR activated Sepharose 6-B and used for removal of somatostatin in hypothalamic fractions, thereby revealing GH-RH activity otherwise concealed. BIBLIOGRAPHIC REFERENCES: Setalo, G., S. Vigh, A.V. Schally, A. Arimura, and B. Flerko. LHRH-Containing Neural Elements in the Rat Hypothalamus. Endocrinology, 96: 135-142, 1975. Hokfelt, T., S. Efendic, C. Hellerstrom, O. Johansson, R. Lift, and A. Arimura. Cellular Localization of Somatostatin in Endocrine-Like Cells and Neurons of the Rat with Special References to the A1-Cells of the Pancreatic Islets and to the Hypothalamus. Acta Endocrinologica, 80: Supplement #20: 5-41, 1975.